Domains, immunoglobulin

Rief M, Gautel M, Oesterhelt F, Fernandez J M and Gaub FI E 1997 Reversible unfolding of individual titin immunoglobulin domains by AFM Science 276 1109... 

Richardson, J.S., et al. Similarity of three-dimensional stmcture between the immunoglobulin domain and the copper, zinc superoxide dismutase subunit. 

All immunoglobulin domains have similar three-dimensional structures... 

T-cell receptors have variable and constant immunoglobulin domains and hypervariable regions... 

Many other cell-surface proteins involved in immunological recognition utilize immunoglobulin-like domains as structural elements. Immunoglobulin domains have been classified into five types, namely V (like antibody variable... 

Lu, H. Isralewitz, B. Krammer, A. Vogel, V. Schulten, K., Unfolding of titin immunoglobulin domains by steered molecular dynamics simulation, Biophys. J. 1998, 75, 662-671... 

Adhesion proteins in this group contain an immunoglobulin domain that is composed of 90-100 amino acids arranged in a sandwich of two sheets of antiparallei strands. Some members of this family also contain fibronectin type III—like domains in addition to the immunoglobulin domain. Immunoglobulin-related adhesion proteins either can exist as transmembrane structures or can be attached to cell membranes via glycosyl phosphatidylinositol links (B4, R5). 

One of the most widely studied molecules from this group of adhesion proteins is N-CAM (B4). N-CAM contains type III fibronectin domains in addition to the immunoglobulin domains. N-CAM also forms covalent associations with poly-sialic acid. This modified form of N-CAM may exert a repulsive force through its high negative surface charge. This, in turn, would lessen cell adhesion and allow invasion. 

However, only the extracellular domains immediately adjacent to the cell membrane and the (32 microglobulin peptide have clear homology with the immunoglobulin domains. The al and ct2 segments of class I and the al and (31 domains in class II have quite an unusual structure. Class I molecules are present on virtually every cell in the body, the most notable exception being the syncytial trophoblast of the placenta. Class II expression is far more restricted B cells, dendritic cells which present antigen to T cells, and macrophage express abundant class II molecule on their surfaces. However, most other tissues can be induced to express class II molecules under the influence of soluble mediators such as 7-interferon. 

Fig. 2. Examples of the structures of protein domains and repeats. The images were generated using Molscript (Kraulis, 1991). (A) Immunoglobulin domain (PDB identifier ltlk) (Holden et al1992), (B) A zinc finger domain with coordinated zinc ion (PDB identifienlzaa) (Pavletich and Pabo, 1991). (C) A /3-propeller domain composed of seven WD40 repeats (PDB identifier lgp2) (Wall et al., 1995), (D) An elongated domain of variant leucine-rich repeats (PDB identifienllrv) (Peters et al., 1996).

M. Rief, M. Gautel, E. Oesterhelt, M. Eemandez, and H.E. Gaub Reversible Unfolding of Individual Titin Immunoglobulin Domains by Afm. Science 276, 1109 (1997). 

Immunoglobulins are constructed in a modular fashion from several immunoglobulin domains (shown in the diagram on the right in Q form). The H chains of IgG contain four of these domains (V h, C hT C h2, and C h3) and the L chains contain two (C l and V l). The letters C and V designate constant or variable regions. 

Fig. 7. (a) Ribbon drawing of immunoglobulin domain, (b and c) Schematic of the folding topology of the immunoglobulin domain. 

Erickson HP. Reversible unfolding of fibronectin type III and immunoglobulin domains provides the structural basis for stretch and elasticity of titin and fibronectin. Proc Natl Acad Sci USA 1994 91 10114-10118. 

These domains, which are found in the muscle protein titin as well as in fibronectin, resemble immunoglobulin domains but lack disulfide bridges. From Erickson.1173 Figure courtesy of Flarold P. Erickson. 

Q Fibronectin type III domain (motif I) Q MLCK region [] Immunoglobulin domain (motif II) Q Interdomain... 

CD Titin immunoglobulin domain Titin Z-repeat a-Actinin... 

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